The Pit: Developers (Demo version)
In the spike pit, the heads that are stuck on the spikes are those of the game's developers.

The Pit: Santa Claus and other flying objects
At Goro's layer, just before you see Reptile, stand by the lion and look at the moon. Wait a short time to see Santa Claus and his reindeer, a witch, and a rocket ship. There is about a one minute delay between each of them.

Easy 1000 Exp Points!
First obtain the combo ranking of "Toasty". Then immediately press the start button. The words "Toasty 1000" should appear in the middle of the screen and you will be awarded 1000 exp points. The best thing about this trick is, it works every time.

Unlock Kitana
In the MK2 arena level (right before the portal with the two statues in front of it) in the evil monastery, you will see many pillars. Jump on one of them which is half broken and then double jump onto the roof. You will find the secret there.

Unlock Baraka
In the soul tomb portal, got to the area where you have to wall climb. You will see 2 paths. One leads left, the other right. The right path has a statue. Use fist of ruin and break it. Keep going and use the long jump ability across the gap and you will get him.

Unlock Johnny Cage
In the wu-shi academy where everything is burning. Go to the very right of the gate and jump onto the roof of the house. Run to the right and jump. If you did it correctly, you will be on a new platform with a boulder blocking your way.